SPACE-STATION BREADBOARD BETA-GIMBAL ASSEMBLY - THERMAL-VACUUM TESTING AND ANALYSES

The objective of thermal-vacuum testing of the breadboard beta gimbal assembly is to demonstrate that the design can survive the hot-cold en vironment of the space-station mission and to check the fidelity of th e thermal model for the beta gimbal assembly The maximum deviation of the analyses from test data was less than 17 degrees C. Only a few dev iations were over 11 degrees C, and most were within the recommended 1 4 degrees C analysis margin. The predictions of the assembly's specifi c characteristics mere confirmed by the test data. An exact match, how ever, is impossible because the testing boundary conditions are more c omplicated than on-orbit flight conditions. Also, there are uncertaint ies about the details of the thermal model. The black and Kapton(R) ad iabatic coupons confirmed that the chamber wall was at -118 degrees C instead of -157 degrees C. The black coupons are recommended for absor bed-flux measurement because a blackbody is the easiest and most accur ate of all coatings to analyze. Using Kapton and bare aluminum coupons is not recommended until a better thermal-radiation solver is availab le. The test results also indicated the two different heat-sink design s, back-to-back and side-to-side, for the coupon yield no significant difference because of the thermocouple design.